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The reaction was reported by Nikolai Kischner in 1911 [3] and Ludwig Wolff in 1912. [4] Scheme 1. Wolff-Kishner Reduction. In general, the reaction mechanism first involves the in situ generation of a hydrazone by condensation of hydrazine with the ketone or aldehyde substrate.
When derived from hydrazine itself, hydrazones condense with a second equivalent of a carbonyl to give azines: [11] R 2 C=N−NH 2 + R 2 C=O → R 2 C=N−N=CR 2 + H 2 O. Hydrazones are intermediates in the Wolff–Kishner reduction. Hydrazones are reactants in hydrazone iodination, the Shapiro reaction, and the Bamford–Stevens reaction to ...
Hydrazine is used in the Wolff–Kishner reduction, a reaction that transforms the carbonyl group of a ketone into a methylene bridge (or an aldehyde into a methyl group) via a hydrazone intermediate.
The Shapiro reaction or tosylhydrazone decomposition is an organic reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of organolithium reagent. [1] [2] [3] The reaction was discovered by Robert H. Shapiro in 1967. [4]
The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. [1] [2] The reaction was discovered in 1883 by Emil Fischer. Today antimigraine drugs of the triptan class are often synthesized by this method. The Fischer ...
Pyrazoles are synthesized by the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation: [6] Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine (Knorr-type reactions). [7] For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole: [8]
Hydrolysis is the reverse reaction of formation with regeneration of the carbonyl compound. In the Shapiro reaction tosylhydrazones are used as a leaving group in elimination reactions. This reaction requires a strong base. If sodium methoxide is used as the base the reaction is called a Bamford–Stevens reaction.
This solution is used to detect ketones and aldehydes. A positive test is signalled by the formation of a yellow, orange or red precipitate of the dinitrophenylhydrazone. Aromatic carbonyls give red precipitates whereas aliphatic carbonyls give more yellow color. [2] The reaction between DNPH and a generic ketone to form a hydrazone is shown below: